Ecdysteroids in nemerteans: Presence and physiological role

Ecdysteroids were detected in the phylum Nemertea and their physiological role was studied. Radioimmunoassay (RIA) measurements showed ecdysteroid concentrations ranging from 1–47 pg/mg wet weight in several nemertean species from the orders Palaeonemertea, Heteronemertea, and Hoplonemertea. High-performance liquid chromatographic (HPLC) analysis of Paranemertes peregrina displayed peaks of RIA activity with retention times similar to those of authentic ecdysone and 20-hydroxyecdysone standards. Fluctuating ecdysteroid titers were observed in the various life stages of Carcinonemertes errans with the highest concentrations (47 pg/mg wet weight) found in gravid females. RIA of HPLC fractions of Carcinonemertes errans eggs indicated the presence of ecdysteroids (105 pg/mg wet weight). Alterations in the growth of juvenile, male, or female C. errans were not observed when the worms were exposed to 10^–7. 10^–6, or 10^–5 M 20-hydroxyecdysone. However, the eggs of C. errans appeared to be stimulated by 20-hydroxyecdysone. Shorter hatching times were observed in the egg strings exposed to hormone (10^–7 to 10^–5 M) compared to sea water and cholesterol (10^–11 and 10^–9 M) controls. Possible physiological roles and the evolutionary significance of ecdysteroids in nemerteans are discussed.